An AR-15 assault rifle. The same used during the Friday attack in Aurora, Colorado.

In the worst mass shooting in Colorado since Columbine, a gunman opened fire early Friday in a packed showing of “The Dark Knight Rises” in Aurora. Twelve are known dead and 59 are reported injured. Police have one suspect in custody, James Eagan Holmes, 24. So far, no motive for the killings has been disclosed.

The president expressed his regret Saturday in a weekly White House address saying, “They had hopes for the future and dreams that were not yet fulfilled. And if there’s anything to take away from this tragedy, it’s a reminder that life is fragile.”

What happened that night? The suspect propped open a parking lot door at the Century 16 Cinema, retrieved his gear from outside, donned a gas mask and bulletproof armor, and detonated two smoke bombs. He then began spraying a stunned crowd of movie-goers with bullets. Additional injuries occurred in the panic to escape. That’s according to a federal investigator speaking to The Associated Press on condition of anonymity.

Aurora Police Chief Dan Oates told Reuters that Holmes had a AR-15 semi-automatic rifle, a shotgun and a pistol. The police arrived at the scene within 90 seconds of the first emergency call. Holmes was arrested minutes later without a struggle in the parking lot after exiting the theater.

A woman and child approach a sign near the Century 16 theater where a gunman killed 12 people. The pair left flowers next to the sign. Source: Ted S. Warren/AP.

Near that exit now is a makeshift memorial. A sign erected over a bed of bouquets reads, “7/20. Gone Not Forgotten.” A group of pastors led a teary vigil nearby for about 350 people Saturday. KUSA-TV said at least 26 victims of the shooting remained hospitalized Saturday, nine in critical condition. That included a 4-month-old, already released from the hospital, and a 6-year-old being treated for a bullet to the face at Children’s Hospital Colorado.

Police say Holmes was a quiet boy with a once promising academic career. A scholarship winner, he graduated at the top of his class at the University of California-Riverside. He moved to Colorado last year to attend the doctoral program in neuroscience at University of Colorado-Denver. There his struggles began, leading to his dropping out this Spring.

According to The New York Times, neighbors described Holmes as a solitary figure. They complained of his blasting loud music at night. They also said he would block up his windows with newspaper so nobody could see into his apartment.

“We’ve become aware that the suspect over the last four months received a high volume of deliveries to both his work and home addresses,” Police Chief Oates said Saturday afternoon at a press conference. “This begins to explain how he got his hands on all the magazines and ammunition. We also think it begins to explain some of the materials he had in his apartment.”

According to Oates, Holmes purchased 6,000 rounds of ammunition online, including a 100-round magazine for the AR-15 assault rifle. Authorities are conducting a cautious investigation of Holmes’ dwelling.

Deputy Aurora Fire Chief Chris Henderson told the AP, “It’s a pretty extensive booby trap. We’re not sure what it’s attached to. There are trip wires. There are three containers and we don’t know what’s inside.”

CNN reported technicians worked to clear the suspect’s apartment with the help of a robot, using it to handle traps, wires and possible incendiary devices. Two devices were intentionally detonated at the site. Police said all hazards had been removed by Saturday evening.

Kaitlyn Fonzi, 20, who lives in the apartment below Holmes’, had a close call. She told the AP she heard loud techno-like music coming from upstairs around midnight. She contacted police only to be told that they were busy with a shooting and didn’t have time to respond to a noise complaint. She then went upstairs to find the door apparently unlocked, however she didn’t enter.

“I yelled out and told him I was going to call the cops and went back to my apartment,” Fonzi said.

Fonzi was later shaken to discover the apartment was trip-wired with explosives.

“I’m concerned if I had opened the door, I would have set it off,” she mused. She believes the music to have been on a timer. It started around the time of the shootings.

The FBI has found no evidence linking the Aurora shootings to any terrorist group.